Using 8155 in 51 MCU System

Introduction: The RAM storage space and number of pins of the microcontroller itself are often insufficient. When there is not much need for external expansion, the 8155 chip is the first choice.

An 8155 can provide 256 bytes of RAM, 3 parallel IO interfaces and a 14-bit timer.

The 8155 also has an internal address latch. If you just need to expand the 8155, you can omit the commonly used address latch 74LS373.

Next, write a program that uses the microcontroller's own resources to drive 16 LEDs in a pipeline.

Then, modify it to be driven by 8155.

The assembly language program for using the 51 single-chip microcomputer to drive 16 LED flowing lights is as follows.

;=========================================================

;16 LEDs are connected to P0 and P2.

ORG0000H

START:

MOV30H,#254;On-chip RAM

MOV31H, #255; 30H31H has only one low level

;-------------------------------------

MOVR2,#16;Loop 16 times

LOOP:

MOVP0,30H; output to LED

MOVP2,31H

CALLDLY200MS; Delay

CALLSHIFT_L; shift

DJNZR2, LOOP; loop 16 times

SJMPSTART; Start from the beginning again

;-------------------------------------

SHIFT_L: Shift 16-bit number one bit to the left

MOVA,30H

RLCA; high shift into Cy

MOV30H,A

;---------------

MOVA,31H

RLCA;Cy moves into the low bit, and the high bit moves into Cy

MOV31H,A

;---------------

MOVA,30H

MOVACC.0,C; write Cy (high bit) to low bit

MOV30H,A

;---------------

RIGHT

;-------------------------------------

DLY200MS:; Delay 200ms, error 0us

MOVR6,#197;

DL0:

MOVR7,#250;1

DJNZR7,$;2*250=500

DJNZR7,$;2*256=512

DJNZR6,DL0;(1+500+512+2)*197=199955

MOVR7,#19;1

DJNZR7,$;2*19=38

NOP;1

RIGHT;1+199955+1+38+1+2=199998

;-------------------------------------

END

;========================================================

The circuit corresponding to the above program is too simple, so the illustration is not shown here. Readers can draw the diagram themselves.

When an 8155 is added to the circuit, the circuit can be connected as follows:

In the figure, since P2.7 and P2.0 are used to connect to CS and IO/M, the interface address and memory address of 8155 are:

;I/O address:

COMMANDEQU7F00H

PORTAEQU7F01H

PORTBEQU7F02H

PORTCEQU7F03H

TIMER_LEQU7F04H

TIMER_HEQU7F05H

;MEM address:

;7E00H~7EFFH

Therefore, the previous running light program needs to be modified as follows:

;=========================================================

;51 single chip microcomputer water lamp (16 lamps)

;P0,P2 external 16 LEDs - changed to PA,PB

;30H,31H on-chip RAM - changed to off-chip

ORG0000H

START:

MOVDPTR,#COMMAND

MOVA,#00000011B;PA mode 0 output, PB mode 0 output

MOVX@DPTR,A

INCDPTR;Go to PA

MOVA,#00110011B; Test common anode 7-segment digital tube

MOVX@DPTR,A

INCDPTR; Go to PB

MOVA,#00001111B

MOVX@DPTR,A

;MOV30H,#254;－－Change to 7E30H

;MOV31H,#255;－－Change to 7E31H

MOVDPTR,#7E30H

MOVA,#254

MOVX@DPTR,A

MOVDPTR,#7E31H;RAM7E30H7E31H

There is only one low level in MOVA,#255;

MOVX@DPTR,A

;-------------------------------------

MOVR2,#16;Loop 16 times

LOOP:

;MOVP0,30H; output to LED

;MOVP2,31H

MOVDPTR,#7E30H

MOVXA,@DPTR

MOVDPTR,#PORTA

MOVX@DPTR,A

MOVDPTR,#7E31H

MOVXA,@DPTR

MOVDPTR,#PORTB

MOVX@DPTR,A

CALLDLY200MS; Delay

CALLSHIFT_L; shift

DJNZR2, LOOP; loop 16 times

SJMPSTART; Start from the beginning again

;-------------------------------------

SHIFT_L: Shift 16-bit number one bit to the left

;MOVA,30H

MOVDPTR,#7E30H

MOVXA,@DPTR

RLCA; high shift into Cy

;MOV30H,A

MOVX@DPTR,A

;---------------

;MOVA,31H

MOVDPTR,#7E31H

MOVXA,@DPTR

RLCA;Cy moves into the low bit, and the high bit moves into Cy

;MOV31H,A

MOVX@DPTR,A

;---------------

;MOVA,30H

MOVDPTR,#7E30H

MOVXA,@DPTR

MOVACC.0,C; write Cy (high bit) to low bit

;MOV30H,A

MOVX@DPTR,A

;---------------

RIGHT

;-------------------------------------

DLY200MS:; Delay 200ms, error 0us

MOVR6,#197;

DL0:

MOVR7,#250;1

DJNZR7,$;2*250=500

DJNZR7,$;2*256=512

DJNZR6,DL0;(1+500+512+2)*197=199955

MOVR7,#19;1

DJNZR7,$;2*19=38

NOP;1

RIGHT;1+199955+1+38+1+2=199998

;-------------------------------------

END

;=========================================================

In the original program, all instructions for reading and writing 30H and 31H are changed to reading and writing external RAM.

All instructions for outputting P0 and P2 are changed to outputting to off-chip PA and PB.

Written in this way, the length of the program has nearly doubled. Haha, there is no other way, I have to do this.

After modification, you can use the resources of 8155 to conduct the running light experiment.

The effect shown is that only one LED is glowing, which is relatively simple, so I won’t illustrate it here.